DoB from IGI:
John Boyd Pedigree  Birth:  About 1757   Of Callius, , Londonderry, Ireland

DoB from aged 72 at death as recorded in the death notice in the Londonderry Sentinel.

DoD from death notice in the Londonderry Sentinel.

And Aghadowey parish church:
56 Boyd
Erected in memory of
John Boyd Junr, late of Collins, who departed this life, 22 June 1833, aged 27 years
also his father, William Boyd, who died 30 March 1848, aged 72 years 

DoB from age 89 at death in 1868 according to his gravestone in Ballylintagh Presbyterian Church.

Source: Civil Death Record - 23 Dec 1868 at Ballybritton, Aghadowey, Hugh Boyd, widower, 89, Labourer, Gangrene of feet 6 weeks certified, Elizabeth Boyd (marked) PAD of Ballybritton.

Also: broken gravestone in Ballylintagh Presbyterian Church, where he is given as aged 89 at death in 1868.

Source LG via MB - lineage of John of Lismoyle.

Source LG via MB - lineage of John of Lismoyle.

From Agha CofI graveyard:
207 Boyd
Old stone, really nice, easy to read
Erected by
John and Thomas Boyd of Boston USA in memory of
their mother, Jane Boyd, who departed this life, 27 December 1852, aged 56 years
their father, Thomas Boyd, stone broken in half here
Killykergan, who departed this life, 11 February 1859, aged 72 years